There is some confusion when we talk about the cartilage in the knee joint, as there are two types: Articular cartilage and the Meniscus. A brief summary of the two can be found below.
Articular cartilage is the ultra smooth covering found on the ends of bones within a joint. It is an integral capping of the bone and is analogous to the tread on a car tyre. It undergoes wear and tear through life and this process may be accelerated in some individuals for a variety of reasons leading onto arthritis.
If a car is driven badly with fast cornering and lots of skids, then the tyres will wear very quickly. Similarly if the knee undergoes lots of injuries throughout its life, then the cartilage may wear more quickly. However exercise is essential for healthy cartilage as the nutrition the cartilage needs is dissolved in the joint fluid and gets “pumped” into the cartilage during movements. Excessive loads and malaligned wheels also cause tyres to bald quickly, and likewise being excessively overweight and having malalignment in the limb can cause accelerated cartilage wear.
As cartilage wears, it becomes roughened, and starts to fray. It may give rise to catching and creakiness within the knee joint.
The picture below illustrates a traumatic lesion of the articular cartilage
Keyhole procedures to address cartilage wear include chondroplasty (shaving the cartilage to give it a smoother finish), and in areas where there is complete wear down to bare bone, microfracture can be performed (see illustration below). Microfracture involves making small holes in the bone at regular intervals to create a surface clot, which over time matures into fibrocartilage, and resurfaces the area of bare bone.
In the picture below, the bare bone lesion on the joint surface is being "microfractured"
In the photo below the appearance of the joint after microfracture is shown with multiple holes in the worn surface and blood oozing through the holes.
· Cartilage grafting is a very specialised procedure, usually done in two stages. Cells from the knee are harvested in the first stage, and grown in a labarotory before being transplanted back into the knee (second stage) with some form of specialised membrane.
· Osteotomy is realignment of the bones around the knee joint to off-load the worn out part of the joint.
The meniscus or "footballers cartilage" exist as a pair in each knee, one on the inner side of the knee and the other at the outer side. They work like shock absorbers and cushions to spread the load in the knee joint. They are semicircular C shaped structures that resemble a crescent moon, and were once named semi-lunar cartilages for this reason. A bit like an orange segment, the outer part is thick and the inner part is thin. They have a poor blood supply which usually only exists in the outer portion. They can be torn in twisting injuries or sometimes without noticeable trauma especially in older people.
The picture below is a view of a normal meniscus lying between the articular surfaces of the femur (thigh bone) above and tibia (shin bone) below.
Tears of the meniscus occur frequently, and may result from a twisting injury or a more minor injury in older people. They tend to cause pain localised to one side of the knee, and may give rise to symptoms of catching, locking or giving way. They can be treated with keyhole surgery (arthroscopy).
Arthroscopic (Keyhole Surgery) techniques are employed to treat these tears by removing the unstable portion of the tear. In some instances repairing the meniscus may be possible, but may necessitate some immobilisation, or restricted weight bearing in the post operative period.
Meniscal repair: Notice the stitches inserted into the cartilage